Magnetron anode structure



March 18, 1947. P. SPENCER MAGNETRON ANODE STRUCTURE Filed Dec. 1, 1941 2 Sheets-Sheet l Ira/@1207: Pergyl, 5 972087 9' March 18, 1947. P. SPENCER M m Q ,0//// V m 7% Perc L. Spencer wi J Patented Mar. 18, 1947 MAGNETRON ANODE STRUCTURE Percy L. Spencer, West Newton, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application December 1, 1941, Serial No. 421,145

. Claims.

This invention relates to a magnetron, and more particularly to a magnetron in which there is provided an anode structure having a plurality of arms adjacent the cathode and in which the dimensions of the arms and the associated anode structure determine the frequency of oscillations produced. A magnetron of this kind is intended to oscillate in a predetermined mode between each pair of anode arms so as to generate a predetermined frequency. However, difiiculties have been encountered in that spurious modes of oscillation occurred which introduced frequencies into the output current which differed widely from the desired output frequency and thus decreased the effectiveness and efiiciency of the device.

An object of this invention is to devise a magnetron in which such spurious modes of oscillation are substantially eliminated.

Another object is to eliminate such spurious oscillations by directly electrically interconnecting those points on the anode structure at which loops of oscillations which should have the same phase occur.

A still further object is to accomplish the foregoing in a simple and effective manner.

The foregoing and other objects of this invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawing, wherein:

Fig. 1 is a transverse cross-section of a magnetron embodying my invention taken along line lof Fig. 2;

Fig. 2 is a longitudinal cross-section taken along line 22 of Fig. 1;

Fig. 3 is a perspective view of my novel anode structure before being assembled with the rest of the tube elements; and

Fig. 4 is a cross-section of the anode structure taken along line 44 of Fig. 3.

The magnetron illustrated in the drawings comprises an envelope I which is preferably made of a block of conductive material, such as copper. This block forms the anode of the magnetron. The block has hollow end sections which are covered by caps 2 and 3 likewise of conductive material, such as copper. Between the hollow end sections of the block I is located a central bridging portion 4. The portion 4 is provided with a central bore 5 within which is supported substantially at the center thereof a cathode 6 which may be of the indirectly-heated thermionic type. The cathode 6 is supported by a pair of cathode lead-in conductors 'l and 8 sealed through glass seals 9 and Ill mounted at the outer ends of pipes H and I2 hermetically fastened within 2 the walls of the block I adjacent the upper and lower hollow end sections. A plurality of slots 13 extend radially from the central bore 5, and each of said slots terminates in a circular opening it extending through the bridging portion 4. In

this way the anode structure is provided with a plurality of wedge-shaped arms 24 to 3|, inclusive, the faces of which cooperate as anode sections with the cathode 6.

When such a magnetron is placed between suitable magnetic poles l5 and I6 to create a longitudinal magnetic field and the device is energized, oscillations are set up. These oscillations may be led out from the tube by means of a coupling loop ll extending into one of the cylindrical openings l4 and having one end thereof fastened to the inner wall of said opening. The other end of the coupling loop I1 is connected to a lead wire I8 which passes through a glass seal l9 mounted at the outer end of a pipe 20 likewise hermetically fastened through the wall of the envelope I. An additional conducting pipe 20 may be fastened to the pipe 20 outside of the seal l9 so as to form with the lead-in conductor I8 a concentric line through which the high frequency oscillations generated by the magnetron may be conducted to a suitable utilization circuit.

The magetron may also be provided with an additional pipe 2| likewise hermetically sealed through the wall of the envelope l adjacent one of the end sections. The pipe 2| may be provided with a glass bulb 22 sealed to the outer end thereof. The glass bulb 22 contains a quantity of an easily vaporizable metal 23, such as barium, which may serve as a getter for the tube. Thus when the device is evacuated and freed of occluded gases in the usual manner, the gettering material within the bulb 22 may be vaporized by magnetic induction heating or by other externally applied heat to clean up the residual gases within the device.

A capacity exists between the cathode 6 and the face of each of the anode sections 24-3I. Also capacitances exist between the side walls of each of the slots l3. The inner walls of the openings I l constitute inductances. The anode therefore is so designed and spaced relative to the cathode that the inductance and capacitances described constitute circuits which are tuned and thus are resonant at substantially the frequency at which the device is to be operated. The device is intended to operate so that each bore l4 and its adjacent arms form a circuit tuned to the frequency at which each of the other bores M and its adjacent arms oscillate.

It has been found that in magnetrons oi this general type, there has been a tendency for oscillations to be produced not only in accordance with the above desired mode but also in various undesired spurious modes. In accordance with my present understanding of the operation of the device, such spurious modes are due mainly to the following. In the normal mode of oscillation, a loop of voltage will occur at each anode arm 24-3l. However, the voltage variation on each arm will be opposite in phase to the voltage variation on each adjacent arm. 11 we now consider two non-adjacent arms, such as 24 and 26, we see that there is a certain amount of capacity between these arms, and the circuit connecting these arms through the body 1 constitutes a certain inductance. Therefore oscillations could be set up in this circuit which would be of a diflerent frequency from that of the desired mode and in which the voltage phases of the arms 24 and 26 would be opposite to each other. Such opposite phase would result in the occurrence of a periodic voltage difierence between the arms 24 and 26. However, in the desired oscillating mode adjacent anode arms are of opposite voltage phase, and alternate anode arms are in the same voltage phase.

In accordance with my invention I eliminate substantially all spurious modes of oscillation by directly interconnecting alternate anode arms by a conductive path of low impedance. Thus, as shown, for example, in Fig. 1, a ring of copper 32 is set into the upper tips of the arms 24, 26, 28 and 30. The upper tips of arms 25, 21, 29 and 31 are cut away sufllciently to avoid touching the ring 32. In this way the arms 24, 26, 28 and 30 are electrically connected together at those points where substantially the greatest voltage difference would occur during the existence of spurious oscillating modes. Due to the electrical interconnection of these points, such voltage differences are suppressed, and thus such spurious modes of oscillation are substantially eliminated. In order to interconnect the arms 25, 21, 29 and 3| in a similar way, a ring 33 of copper at the opposite end of the bridging member i is set into the lower tips of the arms 25, 21, 29 and 3|, and the lower tips of the arms 24, 26, 28 and 30 are cut away to avoid contact with said ring 33. This is shown, for example, in Figs. 2 and 4.

I have found that when the alternate anode arms are electrically interconnected as described above, substantially no spurious modes of oscillation tend to occur. At the same time there appears to be no substantial interference with the normal mode of oscillation. I have constructed tubes in this way which due to the elimination of spurious modes of oscillation have been capable of generating substantially increased amounts of power with substantially increased eiliciency.

In addition to the particular details as described above, many equivalents will suggest themselves to those skilled in the art. For example, other anode configurations could be utilized and other means for electrically interconnecting the points of similar voltage phase could be adopted.

What is claimed is:

1. An electron-discharge device comprising an electrode structure including a cathode and an anode adjacent thereto and having a plurality of arms each pair or which bounds a cavity and forms an inductance, each of said pair or arms forming a capacitance. said inductances and capacitances forming tuned circuits which are adapted to have oscillations set up therein during operation, each of said arms having a groove therein, the grooves in alternate arms having a lesser depth than the grooves in intervening arms, and a conductor secured in each of said grooves of said alternate arms and passing through the grooves in said intervening arms free of contact therewith.

2. A magnetron assembly having a cathode, and an anode structure adjacent thereto and comprised oi ,a plurality or arms each pair or which form an inductance and a capacitance adapted to oscillate in predetermined primary mode, means connecting alternate arms through a path of low impedance comprising a conductor, secured to each of said alternate arms, and passing freely through grooves in each of the intervening arms.

3. An electron-discharge device comprising: a cathode; an anode structure adjacent said cathode and including a plurality of anode sections; each pair of adjacent anode sections, together with that portion of said anode structure lying therebetween, constituting a cavity resonator; and means, directly interconnecting alternate anode sections and overlying at least portions of intervening anode sections, for maintaining said alternate anode sections substantially equipotential.

4. An electron-discharge device comprising: a cathode; an anode structure adjacent said cathode and including a plurality of anode sections; each pair of adjacent anode sections, together with that portion of said anode structure lying therebetween, constituting a cavity resonator; and low-impedance means directly interconnecting alternate anode sections and overlying at least portions of intervening anode sections, whereby said alternate anode sections are maintained substantially equi-potential.

5. An electron-discharge device comprising: a cathode; an anode structure adjacent. said cathode and including a plurality of anode sections; each pair of adjacent anode sections, together with that portion of said anode structure lying therebetwecn, constituting a cavity resonator; and a conducting ring and strap, having a central opening of appreciable size directly interconnecting alternate anode .sections, whereby the latter are maintained substantially equi-potential.

PERCY L. SPENCER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,417,789. March 18, 1947.

PERCY L. SPENCER It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 4, line 48, claim 5, after the word ring strike out and; line 49, same claim, for size directly read size, and directly; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 13th day of May, A. D. 1947.

LESLIE FRAZER,

First Assistant Commissioner of Patents. 

